In U.S. Pat. Nos. 6,802,820 and 6,802,971 there are disclosed specialized hollow fiber membranes having unique and highly efficient asymmetric fiber wall characteristics capable of separating plasma from whole blood in-vivo by exposing the exterior surface of the fiber to whole blood and directing plasma through the fiber wall. Pumping means is used to create a trans-membrane pressure (TMP) and motivate the flow of fluid from within the in-vivo system, whereby blood plasma is pumped from the patient to a treatment means such as a dialyzer apparatus in which toxic metabolic waste in the plasma is removed. After the plasma is treated for removal of waste products, excess fluids, toxins, and/or other deleterious plasma proteins, the treated plasma is returned and reintroduced to the patients' blood stream. Such methods are referred to as plasma dialysis, ultrafiltration, or blood purification. The aforesaid patents are incorporated herein by reference in their entirety.
In conventional hemodialysis procedures hollow fiber membranes are used in the ex-vivo dialysis and hemofilter cartridges for blood purification. The blood is routed from the body through the center lumen of the hollow fibers in the cartridges and dialysate fluid is routed over the outside walls of the fibers within the cartridge cavity in counter-flow direction to blood flow. Thus, toxin diffusion and ultrafiltration are from inside the fiber lumen to a compartment outside the fiber walls where the ultrafiltrate and toxin-saturated dialysate are collected for further processing and/or disposal.
Conventional hollow fiber membranes commercially used for present hemodialysis, hemo-ultrafiltration, and dialyzer cartridges fabricated from proprietary and non-proprietary polymer compositions generally utilize two types of morphologies: symmetrical and asymmetrical. In a symmetrical composition, the basic morphology or cellular structure and porosity of the fiber wall is uniform from the inner lumen to the outside surface. In asymmetrical compositions, both morphology and pore structures vary from the inner lumen to the outer surface to meet the high pressure requirements of the filter cartridges in which the TMP inside the fiber lumen is high (100-300 mmHg) while the blood flow itself in the fibers is near stagnant (2-300 ml/min/7,000 fibers=0.042 ml/m/fiber). Such conventional fiber membranes generally have poor elongation and breaking strength and are not suitable for the demanding environment of the in-vivo, high blood flow (vena cava=2.5 1/min), low TMP (≦50 mmHg), and unencapsulated environment of plasma extraction devices described by the aforesaid patent applications.